Steps:
1. install VScript Replacer plugin
2. start map c8m4_interior
3. put in console: sm_vs_dump
4. go to local files and open: Left 4 Dead 2\left4dead2\scripts\vscripts\vscripts_dump\c 8m4_elevatorfix.nut
5. save as name c8m4_elevatorfix_custom.nut
6. put this new file in carpet: Left 4 Dead 2\left4dead2\scripts\vscripts\vscripts_custom
7. open file: Left 4 Dead 2\left4dead2\addons\sourcemod\data\vscripts_o verride.cfg
Modify and add within the file (it would look like this without the explanatory text of the vscripts_override.cfg)
I just added a code to tell it to replace the original file with the new one that you created in the c8m4_interior map.
8. save the changes of vscripts_override.cfg
9. change the map to c8m4_interior again.
10. invisible wall removed.
Note: I don't know what consequential effects the map can have by modifying this, so this is just a basical example of how to use the VScript Replacer plugin.